That's the point - melee characters either need to rely on blacksmithing/crafting, or they need to hope they get good drops. Mages don't need either.
Yeah, your source of damage can break. I've actually had it happen in a fight, simply because I didn't notice the durability was getting low. Had to switch to a (far inferior) backup weapon.
Man-At-Arms has 2 hard cc abilities, both of which can be countered by high Bodybuilding, not to mention that there are a fair number of enemies who are immune to knockdown. It has one aoe ability (2, counting phoenix dive, though PD's damage never impressed me). And unlike magic, you cannot reduce the cooldown on MaA abilities.
I'm not saying that warriors are valueless. Just that they have lower value. You can replace a warrior with a rogue or a ranger, and still have high single target damage. You cannot remove a mage without losing a TON of utility.
Imagine a party of 4 people.
One pure warrior
One pure ranger
One pure rogue
One pure mage
Now lets say you have to lose one of them. Which one is most expendable?
My answer would be "anyone but the mage".
